Apparatus and method to merge and align data from distributed memory controllers

ABSTRACT

We describe a system and method to merge and align data from distributed memory controllers. A memory system includes a command bus to transmit a predetermined memory access command, and a memory interface to manipulate data from at least two memory channels, each memory channel corresponding to a portion of a distributed memory, responsive to the predetermined memory access command. The memory interface includes a plurality of memory controllers coupled to the command bus, each memory controller being operable to control a corresponding memory channel responsive to the predetermined memory access command, and a push arbiter coupled to each memory controller. The push arbiter being is operable to merge and align data retrieved responsive to each split read align command.

FIELD OF THE INVENTION

This invention relates to accessing a distributed memory and, morespecifically, to merging and aligning data retrieved by distributedmemory controllers.

BACKGROUND OF THE INVENTION

Microprocessors, digital signal processors, digital imaging devices, andmany other types of digital data processing devices rely on a memorysystem to store data and/or instructions needed by the processingdevice. FIG. 1 depicts a typical memory system configuration 100. Memorysystem 100 comprises a memory 140 to store digital data and memorycontroller 110 to control access to memory 140. An address/command busand a data bus transmit memory signals, e.g., on set of signal lines,between memory controller 110 and memory 140. Memory signals fallgenerally into one of several categories including data signals, addresssignals, command signals, and the like. Data signals carry the actualdata that will be stored in, or retrieved from, memory 140, and passacross data bus. Address signals specify the location within memory 140where data is to be read from or written to. Command signals instructmemory 140 as to what type of operation is to be performed, e.g., reador write.

A processing device 50 issues data store and retrieve requests to memorycontroller 110. The processing device 50 may be a processor or anydevice capable of processing or manipulating electronic signals. Thememory controller 110 acts as an intermediary for the exchange of databetween processing device 50 and memory 140. For instance, when theprocessing device 50 issues a retrieve request, the memory controller110 retrieves data from memory 140 and provides the retrieved data toprocessing device 50. The memory controller 110 retrieves data frommemory 140 over the data bus by providing appropriate address andcontrol signals to the memory 140 over the address/command bus.

As processing devices become faster and more powerful, the increaseddemands placed on them generally translate to a need for larger andfaster memory systems. FIG. 2 shows one memory system implementation 200that addresses the increased demands. A distributed memory 220 containsmultiple memories 140, 150, and 160, each to store digital data within apredetermined address space. Each address space may be a predeterminedaddress range or multiple interleaved ranges within a monolithic memoryspace. Or each address space may address space separately located inphysically distinct memories. For ease of programmability and tomaintain backward capability of memory system 200, processing device 50typically perceives distributed memory 220 as one monolithic memoryspace regardless of the actual configuration.

Memory interface 210 comprises memory controllers 110, 120, and 130 thatcontrol access to memories 140, 150, and 160, respectively, where eachmemory access path is known as a memory channel. When processing device50 stores or retrieves data from address space corresponding to memory140, processing device 50 issues a data store or a retrieve request tomemory controller 110, where memory controller 110 acts as anintermediary for the exchange of data between processing device 50 andmemory 140. Memory controllers 120 and 130 perform similarly to memorycontroller 110 with respect to data exchanges between processing device50 and memories 150 and 160, respectively, when device 50 issues a datastore or a retrieve request. By increasing the number of memory channelsand by distributing memory 220, memory system 200 allows processingdevice 50 to perform multiple independent memory accesses to memories140, 150, and 160, thus increasing the throughput (speed) and size ofthe memory system 200.

Memory system 200, however, can have disadvantages. Among thesedisadvantages is when processing device 50 requests data retrieval andshift spanning multiple channels, where independent shifting of dataretrieved from each channel causes erroneous data to be provided to theprocessing device 50. This problem may commonly occur when storing andretrieving large blocks of contiguous data, particularly networkingapplications such as packet header processing.

FIG. 3 shows an illustration of this problem. Distributed memory 220contains data B0-BF stored between two memory channels, data B0-B7within memory 140 and data B8-BF within memory 150. Data retrievalspanning multiple channels is typically performed by processing device50 issuing a first request to memory controller 110 to retrieve dataB0-B7 and a second request to memory controller 120 to retrieve dataB8-BF. Upon receipt of the requests, memory controllers 110 and 120independently retrieve the corresponding data and provide it toprocessing device 50 in the form shown in diagram 310.

Diagram 320 shows the form data B0-BF should be provided to processingdevice 50 when performing data retrieval with a corresponding shift by2, where each X denotes a filler byte of data. X bytes can typically beskipped by processing device 50 when they are inserted at the beginningor end of the retrieved data, however, when added elsewhere detrimentalresults may occur during processing of the retrieved data. When dataretrieval spanning multiple channels with a corresponding shift by 2 isperformed in memory system 200, data B0-BF is provided in the form shownin diagram 330, where X bytes are inserted in the middle of theretrieved data. Accordingly, a need remains for a method and apparatusto merge and align data retrieved by distributed memory controllersprior to providing the data to a processing device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reading the disclosure withreference to the following drawings.

FIGS. 1 and 2 illustrate memory systems.

FIG. 3 is a graph of multi-channel data retrieval using the memorysystem of FIG. 2.

FIG. 4 is a block diagram of a multi-channel distributed memory systemaccording to an embodiment of the invention.

FIG. 5 is a block diagram of memory controller within the multi-channeldistributed memory system of FIG. 4.

FIG. 6 is an example flow chart for operation of each memory controllerof FIG. 4.

FIG. 7 is a block diagram of a push arbiter within the multi-channeldistributed memory system of FIG. 4.

FIG. 8 is an example flow chart for operation of the push arbiter ofFIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

This is a multi-channel distributed memory system implementation. Werecognized that memory systems employing distributed memory havedifficulty retrieving and shifting data spanning multiple memorychannels, as the shift functionality requires a merging of dataretrieved through two independent memory channels. By improving eachmemory controller and adding a push arbiter to a memory interface,merging and aligning data retrieved through multiple channels isachieved with minimal communication between the memory controllers.

FIG. 4 is a block diagram of a multi-channel distributed memory system400 according to an embodiment of the invention. Distributed memory 410contains a plurality of memories 410_1 to 410_N, each to store digitaldata within a predetermined address space. Each address space may be apredetermined address range of a memory or located in physicallydistinct memories. Each address space of the memories 410_1 to 410_N maybe interleaved 128 Byte blocks within a monolithic memory.

Memory master 70 may access distributed memory 410 via memory interface420. Memory master 70 may be a processing device, a Peripheral ComponentInterconnect (PCI) device, or any other device capable of processing ormanipulating electrical signals. For ease of programmability and tomaintain backward capability of multi-channel distributed memory system400, memory master 70 typically perceives distributed memory 410 as onemonolithic memory space, regardless of the actual configuration.Although only one memory master 70 is shown coupled to memory system400, in other embodiments, memory system 400 may support multiple memorymasters 70.

An embodiment of memory interface 420 will be explained with referenceto FIGS. 4-8. Referring to FIG. 4, memory interface 420 comprises aplurality of memory controllers 500_1 to 500_N and a push arbiter 700.Push arbiter 700 is coupled between memory master 70 and memorycontrollers 500_1 to 500_N, where each memory controller 500_1 to 500_Ncontrols access to memories 410_1 to 410_N, respectively. Upon receptionof a memory access command from memory master 70 over a shared commandbus, each memory controller 500_1 to 500_N determines the type of thecommand, e.g., Read, Write, Read_Align, or the like, and the portion ofdistributed memory 410 to be accessed. A Read_Align command requestsmemory interface 420 retrieve data from distributed memory 410 and shiftthe retrieved data prior providing the data to memory master 70. When aRead_Align command is issued to memory controllers 500_1 to 500_N fordata retrieval from memory 410_1, each memory controller 500_1 to 500_Ndetermines data is to be retrieved by memory controller 500_1. Uponretrieval of the data by memory controller 500_1, the retrieved data isshifted by push arbiter 700 and provided to memory master 70 responsiveto its initial memory access command.

Since memory master 70 regards distributive memory 410 as a monolithicmemory, each memory access command may be “split” between two or morememory channels. When a split Read_Align command is issued for dataretrieval from memory 410_1 and 410_2, memory controllers 500_1 and500_2 each independently retrieve and “tag” the data from memories 410_1and 410_2, respectively, and provide the tagged data to push arbiter700. Push arbiter 700 subsequently manipulates and provides the taggeddata to memory master 70, where manipulation may constitute merging,aligning, shifting, combining, altering, modifying, or the like, or anycombination thereof.

FIG. 5 is a block diagram of memory controller 500_1 within themulti-channel distributed memory system 400. Referring to FIG. 5, aninterleave logic 510 receives memory access commands from memory master70 over the command bus. Interleave logic 510 may determine whether acommand requests access to a portion of distributed memory 410corresponding to memory controller 500_1. In an embodiment, interleavelogic 510 comprises an address decoder 511 to decode the address portionof the memory access command. When N memory controllers are present inmemory interface 420, where N is a positive integer greater than 1, theaddress decoder 511 may perform a modulo-N reduction on the addressportion of the memory access command to determine, for example, whetherthe command addresses the distributed memory 410 corresponding to memorycontroller 500. The address decoder 511 may decode the address in avariety of manners to determine any number of conditions.

An inlet command queue 520 provides memory access commands todistributed memory 410, where queue 520 receives each command upon thedetermination that the command requests access to a portion ofdistributed memory 410 corresponding to memory controller 500_1. Whenprovided with a retrieval command by inlet command queue 520, e.g., Reador Read_Align, memory 410 provides data corresponding to the retrievalcommand to a push queue 530, where push queue 530 provides the retrieveddata to push arbiter 700.

Memory controller 500_1 maintains a scoreboard free-list 540 populatedwith scoreboard entries, each entry to facilitate push arbiter 700merging and aligning data retrieved with a split Read_Access command.The merging and aligning of the retrieved data requires a shift in theretrieved data, e.g., a shift of 1-3 bytes. In an embodiment, thescoreboard free-list 540 is a queue to hold unallocated scoreboardentries. Each memory controller 500_1 to 500_N may maintain a scoreboardfree-list 540, where each free-list 540 is updated upon receipt of eachsplit Read Access command over shared command bus.

FIG. 6 is an example flow chart 600 for operation of the memorycontroller 500_1 upon reception of a split Read_Align command over ashared command bus. According to a block 610, a memory controller 500_1receives a split Read_Align memory access command. Although interleavelogic 510 is shown receiving memory commands directly from the commandbus, in other embodiments an intermediate receiver may receive thememory access commands and provide each to interleave logic 510.

According to a next block 620, memory controller 500_1 determines theportions of distributed memory 410 associated with the split Read_Aligncommand. In an embodiment, address decoder 511 within interleave logic510 decodes the address portion of the split Read_Align command todetermine the portions of distributed memory 410 to access responsive tothe split Read_Align command. When N memory controllers are present inmemory interface 420, where N is a positive integer greater than 1, theaddress decoder 511 may perform a modulo-N reduction on the addressportion of the memory access command to determine whether the commandaddresses the distributed memory 410 corresponding to memory controller500_1. As before, the address decoder 511 may decode the address in avariety of manners to determine any number of conditions.

A next decision block 625 determines whether one of the associatedportions of distributed memory 410 corresponding to the memorycontroller 500_1. When it is determined the memory access command doesnot request access to a portion of distributed memory 410 correspondingto the memory controller 500_1, according to a next block 630, memorycontroller 500_1 removes and discards a scoreboard entry from thescoreboard free-list 540. By removing and discarding the scoreboardentry, memory controller 500_1 updates scoreboard free-list 540 tocoincide with the allocation of the scoreboard entry by another memorycontroller. In an embodiment, the scoreboard entry is the entry at thehead of a free-list queue.

When, at decision block 625, it is determined the memory access commandrequests access to a portion of distributed memory 410 corresponding tothe memory controller, according to a next block 640, memory controller500_1 allocates a scoreboard entry from the scoreboard free-list 530 tothe split Read_Align command. In an embodiment, interleave logic 510removes the scoreboard entry from the free-list 530 and adds it to thesplit Read_Align command as it is being provided to inlet command queue520. Alternatively, interleave logic 510 may add the scoreboard entry todata retrieved in accordance with the split Read_Align command. Thescoreboard entry may be the entry at the head of a queue.

According to a next block 650, memory controller 500_1 retrieves datafrom the corresponding portion of distributed memory 410 according tothe split Read_Align command. Interleave logic 510 provides the splitRead_Align command to inlet command queue 520, where the command isprovided to the corresponding portion of distributed memory 410. Dataretrieved in accordance with the split Read_Align command is received atpush queue 530, and in an embodiment, contains information regarding thenumber of bytes push arbiter 700 is to shift the data. In anotherembodiment, the scoreboard entry indicates the number of bytes pusharbiter 700 is to shift the data.

According to a next block 660, memory controller 500_1 provides theretrieved data allocated with the scoreboard entry to the push arbiter700. In an embodiment, the push queue 530 provides the data when itreaches the head of the queue.

Referring to FIGS. 4 and 5, since each memory controller 500_1 to 500_Nreceives the same memory access commands, each corresponding scoreboardfree-list 540 is updated with each split Read_Align command from memorymaster 70, and deallocation signal from push arbiter 700. Thisindependent updating of corresponding scoreboard free-lists 540 allowsmemory controllers 500_1 to 500_N to provide scoreboard entries to pusharbiter 700 with minimal communication with each other. Furthermore, theability of each memory controller 500_1 to 500_N to receive the samecommand and determine which command applies to each portion ofdistributed memory 410, eases the burden on memory master 70 andimproves the backward capability of memory system 400.

FIG. 7 is a block diagram of a push arbiter 700 within the multi-channeldistributed memory system 400. Referring to FIG. 7, a plurality of inputqueues 710_1 to 710_N receive data retrieved by memory controllers 500_1to 500_N, respectively. While the number of input queues is shown asequal to the number of memory controllers, in other embodiments a pusharbiter 700 with any number of input queues may be implemented.

Aligner 730 provides data within input queues 710_1 to 710_N to memorymaster 70 and combines data within at least two input queues 710_1 to710_N when directed by scoreboard 720. In an embodiment, aligner 730comprises a plurality of transfer registers, where aligner 730 mergesand aligns data by controlling the data provided to each transferregisters. Each transfer register may contain any number of data bytes,e.g., 4 bytes of data.

Scoreboard 720 may comprise a table populated with scoreboard entries,each entry to indicate when data within input queues 710_1 to 710_N isto be merged and aligned by aligner 730. After reception of retrieveddata by input queues 710_1 to 710_N, scoreboard 720 determines whether ascoreboard entry has been allocated to data in input queues 710_1 to710_N. In an embodiment, when retrieved data allocated with a scoreboardentry is provided to aligner 730, each scoreboard entry is sent toscoreboard 720, where the scoreboard 720 directs aligner 730 to mergeand align retrieved data with the same scoreboard entry.

FIG. 8 is an example flow chart 800 for operation of push arbiter 700.According to a block 810, push arbiter 700 receives data from at leasttwo of memory controllers 500_1 to 500_N. A next decision block 815determines whether the received data has been allocated a scoreboardentry. In an embodiment, scoreboard 720 receives each allocatedscoreboard entry when input queues 710_1 to 710_N provide data allocatedwith the scoreboard to aligner 730.

When it is determined the received data has not been allocated ascoreboard entry, according to a next block 820, where the received datais provided to memory master 70. When, at decision block 815, it isdetermined the received data has been allocated a scoreboard entry,according to a next block 830, push arbiter 700 aligns and merges thedata corresponding to the allocation. In an embodiment, aligner 730merges and aligns data by controlling the data provided to each transferregisters. According to a next block 840, push arbiter 700 provides themerged and aligned data to memory master 70.

According to a next block 850, push arbiter 700 deallocates thescoreboard entry and provides the deallocated scoreboard entry to eachmemory controller 500_1 to 500_N. In an embodiment, the dealloactedscoreboard entry is provided to each scoreboard free-list 540 withinmemory controllers 500_ to 500_N. Although block 840 is shown as beingperformed subsequent to block 850, their order of operation may beconcurrent or reversed.

One of ordinary skill in the art will recognize that the concepts taughtmay be tailored to a particular application in many other advantageousways. In particular, those skilled in the art will recognize that theillustrated embodiments are but one of many alternative implementationsthat will become apparent upon reading this invention description.Although a transfer register implementation for push arbiter isillustrated, those skilled in the art recognize that many equivalentconfigurations can be employed to merge and align data from the memorycontrollers. Such minor modifications are encompassed within theinvention, and are intended to fall within the scope of the claims.

The preceding embodiments are exemplary. Although the specification mayrefer to “an”, “one”, “another”, or “some” embodiment(s) in severallocations, this does not necessarily mean that each such reference is tothe same embodiment(s), or that the feature only applies to a singleembodiment.

-   -   We claim the following.

1. A memory system comprising: a command bus to transmit a predeterminedmemory access command; a memory interface to manipulate data from atleast two memory channels, each memory channel corresponding to aportion of a distributed memory, responsive to the predetermined memoryaccess command.
 2. The memory system of claim 1 where the predeterminedmemory access command is a split read align command.
 3. The memorysystem of claim 1 where the memory interface is operable to align andmerge the data.
 4. The memory system of claim 2 where the memoryinterface comprises: a plurality of memory controllers coupled to thecommand bus, each memory controller being operable to control acorresponding memory channel responsive to the predetermined memoryaccess command; and a push arbiter coupled to each memory controller,the push arbiter being operable to merge data retrieved responsive toeach split read align command.
 5. The memory system of claim 4 whereeach memory controller is operable to allocate a scoreboard entry todata retrieved responsive to the split read align command; and where thepush arbiter is operable to merge the retrieved data responsive to thescoreboard entries.
 6. The memory system of claim 4 where each memorycontroller is operable to identify each of the at least two memorychannels requested by the predetermined memory access command.
 7. Thememory system of claim 4 where the push arbiter is operable todeallocate each scoreboard entry and operable to provide eachdeallocated scoreboard entry to each memory controller.
 8. A memorycontroller comprising: an interleave circuit to receive a memory accesscommand on a bus; and a scoreboard free-list populated with at least onescoreboard entry to indicate data was retrieved from distributed memoryresponsive to the memory access command.
 9. The memory controller ofclaim 8 where the interleave circuit is operable to update thescoreboard free-list responsive to the memory access command.
 10. Thememory controller of claim 8 where the memory access command is a splitread align command.
 11. The memory controller of claim 10 where theinterleave logic is operable to allocate a scoreboard entry from thescoreboard free-list responsive to the split read align command.
 12. Thememory controller of claim 11 where the interleave logic is operable todiscard a scoreboard entry from the scoreboard free-list responsive tothe split read align command.
 13. The memory controller of claim 8comprising: an inlet queue to provide the memory access command to thedistributed memory, the interleave circuit being operable to determinewhether the memory access command corresponds to a first portion of thedistributed memory prior to providing the memory access command to theinlet queue; and a push queue to receive data from the first portion ofthe distributed memory responsive to the memory access command.
 14. Apush arbiter comprising: a scoreboard to detect scoreboard entriescorresponding to data retrieved through at least two memory channels ofa distributed memory, each memory channel associated with a separateportion of the distributed memory; and an assembly unit to merge theretrieved data responsive to the detection.
 15. The push arbiter ofclaim 14 comprising at least one queue to provide the retrieved data tothe scoreboard and the assembly unit.
 16. The push arbiter of claim 15where the at least one queue corresponds to one of the at least twomemory channels of the distributed memory.
 17. The push arbiter of claim14 where the scoreboard is operable to deallocate scoreboard entriesfrom the retrieved data and operable to make available the deallocatedscoreboard entries to at least two memory controllers.
 18. The pusharbiter of claim 14 where the assembly unit is operable to merge theretrieved data allocated with a same scoreboard entry.
 19. A methodcomprising: receiving a memory access command over a command bus;determining a memory portion to be accessed in a distributed memoryresponsive to the memory access command; and updating a scoreboardresponsive to the determining.
 20. The method of claim 19 comprisingretrieving data stored in the memory portion responsive to the memoryaccess command.
 21. The method of claim 19 comprising updating ascoreboard free-list of the scoreboard populated with at least onescoreboard entry responsive to the determining.
 22. The method of claim21 comprising discarding a scoreboard entry from the scoreboardfree-list responsive to the memory access command.
 23. The method ofclaim 21 allocating a scoreboard entry from the scoreboard free-listresponsive to the memory access command.
 24. The method of claim 19comprising retrieving data from the memory portion responsive to thememory access command, where data is allocated a scoreboard entry; andcombining the retrieved data with data retrieve from another memoryportion at a push arbiter responsive to the scoreboard entry.
 25. Themethod of claim 19 comprising receiving a scoreboard entry from a pusharbiter; and updating the scoreboard with a scoreboard entry.
 26. Themethod of claim 25 comprises inserting the scoreboard entry into ascoreboard free-list.
 27. The method of claim 19 comprising decoding anaddress portion of the memory access command.
 28. An article comprisinga computer-readable medium containing computer instructions that, whenexecuted, cause a processor or multiple communicating processors toperform a method comprising: receiving a memory access command over acommand bus; determining a memory portion to be accessed in adistributed memory responsive to the memory access command; and updatinga scoreboard responsive to the determining.
 29. The article of claim 28comprising updating a scoreboard free-list of the scoreboard populatedwith at least one scoreboard entry responsive to the determining. 30.The article of claim 28 allocating a scoreboard entry from thescoreboard free-list responsive to the memory access command.